Markings and seals have long been used to authenticate the nature or provenance of documents and other items. Continuing efforts have been directed to preventing intentional or accidental misuse. For this purpose, two approaches have generally been followed, separately or in combination. One approach is to increase the difficulty of accessing information communicated by the marking. The other approach is to increase the difficulty of physically reproducing the marking.
The first approach generally involves encryption, which has strong and weak points. Typically, the more difficult it is to break a code, the more difficult and complex is the equipment required to utilize the code.
It is well known to provide an encodement in a form that is not readable without the use of specific equipment. The machine readable code or “symbology” may be visible to the eye or invisible, but requires specialized equipment to read and decode. The terms “symbology” or “symbologies” are generally employed to denote spatial patterns of elements, in which each mark has a defined shape and is separated from an adjacent element by a spacing. Information is encoded in the shapes and/or the spacings. The term “symbology” is inclusive of two- and three-dimensional bar codes and other codes. Typically the decoded information output by the reader is used to provide other information by means of a look-up table or the like. The term “look-up table” refers to both a complement of logical memory in one or more computing devices and to necessary equipment and software for controlling and providing access to the logical memory.
The second approach, physical limitations on the reproduction of a marking, is limited by the output provided by a particular technology. At one time, engraving provided an output that was difficult and expensive to reproduce or imitate. With improvements in other printing technologies, engraving is no longer sufficient, by itself, for a great many authentication purposes.
Technologies are known that use compressed fluid solvents to create thin films and particle streams. The term “compressed fluid” and like terms are used herein to refer to both supercritical fluids and other fluids that are compressed, but are not supercritical. For example, U.S. Pat. No. 4,734,227, issued Mar. 29, 1988, discloses a method for depositing solid films or creating fine powders through the dissolution of solid material into a compressed fluid solution and rapidly expanding the solution to create the particles or films.
The use of supercritical CO2 has been suggested as an alternative to organic cleaning solvents, particularly in combination with reverse micelles or microemulsions, as described in Supercritical Fluid Cleaning, J. McHardy and S. Sawan, Eds., Noyes Publications, Westwood, N.J. (1998), pp. 87–120, Chapter 5, entitled “Surfactants and Microemulsions in Supercritical Fluids” by K. Jackson and J. Fulton. U.S. Pat. Nos. 5,789,505; 5,944,996; 6,131,421; and 6,228,826 describe cleaning processes employing carbon dioxide as solvent along with surfactants having CO2-philic portions and hydrophilic or otherwise CO2-phobic portions, wherein the combination of CO2 and surfactant are useful for removing CO2-phobic (including hydrophilic) contaminants from a substrate. U.S. Pat. No. 6,131,421 describes the formation of a reverse micelle system useful for removing hydrophilic contaminants when water is also included with the carbon dioxide and surfactant.
PCT Patent Publication WO 02/45868 A2, discloses a method of creating a pattern on a surface of a wafer using compressed carbon dioxide. The method includes dissolving or suspending a material in a solvent phase containing compressed carbon dioxide, and depositing the solution or suspension onto the surface of the wafer, the evaporation of the solvent phase leaving a patterned deposit of the material. The wafer is prepatterned using lithography to provide the wafer with hydrophilic and hydrophobic areas.
U.S. Pat. No. 6,471,327 discloses methods suitable for printing with particles of organic materials having sizes of less than 30 nanometers. The terms “nanocrystals” and “nanocrystalline” and like terms are used herein to refer to particles having a size in the range of 10 to 30 nanometers. Nanocrystalline particulates have a particle size distribution that has a mean/median particle size of less than 30 nanometers. The terms “bulk crystal” and “bulk particulates” and like terms, refer to particles and particulates that have one or more dimensions greater than 30 nanometers.
Polymorphism is a phenomenon of large (bulk state) organic/molecular crystals. Polymorphism is defined as multiple crystal structures of the same molecular entity (J. Bernstein and J. Henk, Industrial Applications of X-ray Diffraction, Chapter 25, F. H. Chung and D. K. Smith eds., Marcel Dekker Inc., New York, 531–532 (2000)). A polymorphic bulk crystal of a specific organic/molecular material exhibits multiple bulk crystal structures with different physical and mechanical properties, such as solubility, color, absorption, emission, bulk modulus, etc. An example of a material that exhibits polymorphism is tris(8-hydroxyquinoline) aluminum. Three polymorphs identified as α, β, and γ were reported in M. Brinkman et al., Journal of the American Chemical Society, 122, 5147–5157 (2000)) with α and β exhibiting yellowish-green fluorescence and γ exhibiting blue fluorescence when excited with ultraviolet light (M. Braun et al. J. Chem. Phys., 114(21), 9625–9632 (2001)).
The terms “nanomorph” and “nanomorphic particulate” and like terms, are used herein to refer to nanocrystalline particles and nanocrystalline particulates that exhibit changed properties from those of the same particles or particulate in a bulk state. For the purposes of this definition, the same particles or particulates are composed of the same chemical compound or compounds in the same proportions; as determined by starting materials, molecular weights, and elemental compositions, and can be crystalline, semicrystalline, or amorphous. Changes in stereochemistry and the like are not considered. The type and number of nanomorphs exhibited by a particular compound are not direct correlations of the type and number of polymorphs of the same organic/molecular material in bulk crystal. Chemical compounds in nanomorphic materials have molecular weights in the range of 100 to 100,000 daltons.
Organic compounds that form nanocrystalline H- or J-aggregates are used in some silver halide based photographic products. The H- and J-aggregate nanocrystals exhibit unique properties that differ from the properties of the bulk solid. (A. Herz, Photog. Sci. Eng., 18, 323–335 (1974); E. Jelley, Nature, 138, 1009–1010 (1936)) These materials are, thus, nanomorphic.
The following are examples of references disclosing preparation of nanocrystalline materials and compressed fluid printing: U.S. Pat. No. 6,471,327; U.S. Patent Application Publication No. 2003/0121447 A1; U.S. Patent Application Publication No. 2003/0122106 A1; U.S. Patent Application Publication No. 2003/0117471 A1; U.S. Patent Application Publication No. 2003/0107614 A1; U.S. Patent Application Publication No. 2003/0030706 A1; U.S. Patent Application Publication No. 2002/0118246 A1; U.S. Patent Application Publication No. 2002/0118245 A1; all of which are hereby incorporated herein by reference. Other examples are: EP 1 321 303 A1; WO 03/006563 A1; WO 03/053561.
It would thus be desirable to provide authentication methods and apparatus that rely on physical features relating to the preparation of particular materials.